1. Field of the Invention
The present invention concerns a method of and a device for quantifying the morphology and measuring the thickness and its evolution of a localized area of a surface layer of a thin layer structure.
The many applications of the invention include in situ real time control of the fabrication of microsystems such as semiconductors, integrated circuits, for example dimensional control for contour extraction, absolute measurement of the thickness of a layer and its rate of growth (deposition) or removal (etching), etc.
2. Description of the Prior Art
U.S. patent application Ser. No. 930,243 describes a compact system for simultaneous laser interferometric measurement and observation for in situ interferometric measurement of a stack of thin layers in a vacuum treatment chamber. The system includes an observation camera with the optical axis of the objective common to a monochromatic illumination beam and one or two interferometric measurement laser beams.
This prior art document discloses a powerful method suitable for controlling the rate of growth or removal of the surface layer of a thin layer structure. It has some imperfections, however. In particular, the monochromatic illumination beam and the inteferometric measurement laser beam do not have exactly the same wavelength which causes achromatism so that the two light beams can be focused simultaneously only if the objectives are achromatic. Also this method does not allow absolute measurement of the thickness of the surface layer in the area under observation, as it is based on differential interferometric measurement which is repeated modulo one period.
U.S. Pat. No. 4,984,894 (KONDO) discloses a technique for measuring the thickness of the surface layer of a multilayer structure. This technique consists in illuminating the structure with a light beam in the visible spectrum or in the ultra violet spectrum to determine the thickness of the surface layer of the structure by spectral analysis of part of the reflected beam. However, this technique is proposed for use on a microscope which cannot be used in situ to measure the thickness of the layers carrying patterns during their fabrication inside a vacuum chamber. The distance between the structure under observation and the objective of the apparatus is relatively large (usually in the order of 10 cm), which means that a microscope cannot be used.
An object of the present invention is to propose an improved technique for remedying the limitations of the aforementioned prior art techniques and to enable in situ real time observation of the morphology and thickness of a localized area of the surface layer of a thin layer structure.
Another object of the invention is to provide an observation device using this technique which is very small so that it can be integrated into existing equipment for the vacuum fabrication technique for complex thin layer structures.